1. Technical Field
Systems and methods for monitoring valve operation in an internal combustion engine using camshaft position sensing.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine when operating in a reduced displacement mode such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light-to-moderate load conditions, for example. In some engine configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated. Cylinder deactivation may include deactivation of intake valves, exhaust valves, or both depending upon the particular application and engine technology. Various techniques have been developed for activating and deactivating intake and/or exhaust valves that rely on mechanical, hydraulic, electric/electronic or combination devices to implement valve deactivation in response to a command signal from an engine controller.
Under some conditions deactivated valves may continue to operate (open or lift) and/or activated valves may not open when commanded. Such conditions may result in degraded drivability, increased NVH (noise, vibration, harshness), reduced fuel economy, or component degradation, for example. As such, a number of strategies have been developed for monitoring valve operation. For example, one strategy analyzes the period between intake pressure pulses measured by a manifold absolute pressure (MAP) sensor, while another strategy analyzes a knock sensor signal.